In recent years, in concomitance with the reduction in size of electric apparatuses and electronic apparatuses, magnetic cores forming transformers and coils, which are used for the above apparatuses, are required to have characteristics, such as a high magnetic permeability and a low eddy-current loss, at a high frequency. Accordingly, in order to obtain a low eddy-current loss in a high frequency band, the magnetic core is required to have a high electric resistance. As one example of the magnetic core as described above, for example, there has been a powder magnetic core formed in such a way that after a magnetic material is formed into a fine particulate powder, the surface of each particle is covered with an insulating film, and the particles thus treated are processed by compression molding. Compared to the case in which a bulky magnetic material is used, by the powder magnetic core, although the magnetic permeability is decreased, in particular, the electric resistance can be significantly increased, and the eddy-current loss can be remarkably decreased.
Heretofore, a method has been known in which after hydroxides are adsorbed on the surface of pure Fe which is a magnetic material powder by hydrolysis of a metal alkoxide, a sintered body is obtained by pressing the powder thus obtained (for example, see Japanese Unexamined Patent Application Publication No. 09-125111).
In addition, a manufacturing method to obtain a molded powder compact has been known (for example, see Japanese Unexamined Patent Application Publication No. 2012-172172). In this method, after a compaction molding powder in which a metal alkoxide and a mineral containing crystal water are present on surfaces of soft magnetic metal particles and this compaction molding powder are compressed to form a green molded body, this green molded body is annealed to hydrolyze the metal alkoxide and to generate insulating films on the surfaces of the soft magnetic metal particles.